Gray is quoted as stating the following in the report:

"Mac continues its slow gain among Forrester's clients, even without an enterprise strategy. Apple's singular focus on user experience has resulted in some success in the enterprise--without even trying to break into the market,"

Enterprise Mac footprint
The report details that Mac usages has jumped from 1.1 percent in October 2006 to 3.6 percent the next year.  It subsequently jumped to 4.5 percent in June 2008.  Gray believes that enterprise Mac adoption is increasing due to consumer demand, the report states:

"Strong iPod branding and sales have led to greater consumer sales of Apple PCs." "In turn, this has lured enthusiasts and small workgroups with supple IT departments beyond the standard domain of design and media."

Overall, the rise is counter to the traditional belief that Macs are not viable in the enterprise market.  Gray highlights the mindset:

"Enterprises often see Macs as expensive solutions that add unwanted variety to an already complex IT management and support operation, while providing little in additional productivity".

Despite this negative perception of Macs in the enterprise a growing number of firms are considering the use of Macs.  For example, IBM has initiated a Mac Pilot Program which will study moving employees to the Mac.

Gray identifies 3 factors that will drive enterprise Mac adoption
The article highlights the following:
1. Emerging client virtualization solutions shift the focus from standardized hardware to more secure and manageable PC architectures and operations.
2. The success of the iPhone is driving many to improve the end-to-end experience with Macs.
3. Tech Populism drives younger, more tech-savvy workers to buy whatever tools they need, to work smarter, faster, and cheaper.

You can view the complete eWeek article here.

Commentary
I have long held the view that virtualization and Apple's ability to deliver an end-to-end experience are two of Apple's key competitive advantages.  Please see the referenced articles from May 2006 and June 2006 respectively.  Key quotes from those two articles:

"I ... expect businesses and enterprises to give Macs additional consideration as a future hardware purchase."

"This revitalization and re-application of the end-to-end model will ultimately lead to a level of Mac success that has not been seen to date.  In my view, the Mac is about to grow by leaps and bounds.  I've even voiced my expectations of Apple's market share by the end of the OS X Leopard lifecycle.  Integration and ease-of-use is what today's consumer demands.  Apple's approach is able to meet this demand by offering a compelling, complete, and refined total user experience."